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Determination of air drag coefficient of a car by means of coasting

Münch K.

Zeszyty Naukowe Instytutu Pojazdów / Politechnika Warszawska

2012

z. 5/91

27--32

The air drag coefficient will usually determined by wind tunnel experiments. The boundary conditions are fixed and reproducible. The costs of wind tunnel experiments are high and connected with a significant effort. Influence of the “moving street” during the experiment is only difficult to simulate, frequently done by means of a moving belt between the wheels of the car. Therefore at the lab of Thermo-and Fluiddynamics at the Cologne Institute for Automotive Engineering a new test procedure for determination of the air drag coefficient has been developed. A serial production car “Seat Ibiza ST” was tested unchanged and with modified under surface by means of coasting. The car was accelerated up to 120 km/h on a test track (2 km). The deceleration curve due to friction and air drag was measured by a GPS tracking system. By means of a general accepted evaluation procedure (NEDC-coasting) the drag was able to determine. A separation between friction based drag and aerodynamic drag is possible. The measurements indicate a good accuracy. The mistake is less than 5 % related to the origin drag coefficient. Unfortunately the boundary condition must not be changed during the test. That means, that the weather has to be stable, dry, not windy during the tests. An unusable procedure for industrial kind of work with a given time schedule. Therefore wind tunnel tests are still necessary.

Design studies for a city car under aerodynamic aspects

Bechthold F., Beck K., Vogel F., Knorsch T., Schwan A., Münch K.

Zeszyty Naukowe Instytutu Pojazdów / Politechnika Warszawska

2008

z. 5/72

165--170

The student research project describes the definition of specifications for a “City Car”. It will demonstrate the requirements for the power drive as well as for the space saving concept. A first conceptual design has been realized and a model was produced for wind tunnel test in the laboratory for thermo- and fluid dynamics of the Collogne University of Applied Sciences. During the several wind tunnel tests the model was improved concerning aerodynamic aspects. The result will be represented and discussed. The challenge to find a good aerodynamic design for a short City Car will be demonstrated and one possible result will be pointed out.